The invention relates to an injector of a flotation cell, the injector comprising a feed pipe for feeding a fibre suspension flow into the flotation cell, a mixing apparatus for mixing air into the fibre suspension flow and at least one air feed connection arranged before the mixing apparatus for feeding air into the injector.
The invention also relates to a nozzle section of a flotation cell injector.
The invention further relates to a flotation cell for removing ink or impurities from a fibre suspension.
The invention further relates to a method of mixing a fibre suspension flow and air into each other in a flotation cell injector, the injector comprising a feed pipe for feeding a fibre suspension flow into the flotation cell, a mixing apparatus for mixing air into the fibre suspension flow and at least one air feed connection arranged before the mixing apparatus for feeding air into the injector, the method comprising feeding the fibre suspension flow into the injector, dividing the fed fibre suspension flow into partial flows, feeding air to be mixed into the fibre suspension flow into the injector, feeding the partial flows of the fibre suspension flow into the mixing apparatus forming a pre-mixing phase of the injector, whereby air fed into the injector is carried into the pre-mixing phase by the partial flows, and mixing air carried into the pre-mixing phase by the partial flows into these partial flows.
Flotation cells, i.e. flotation containers, are used to remove ink and any impurities from a fibre suspension produced from disintegrated and sorted recycled paper. This process is also called deinking. The purpose of deinking is to obtain as white and clean recycled fibre pulp as possible. Flotation cells are used in flotation deinking, where flotation is performed in cells by adding soap or another flotation stimulating and surface tension preventing chemical as a flotation chemical into a diluted, approximately 1-% fibre suspension. In addition, air is mixed into the fibre suspension. Ink and impurities stick to air bubbles that rise to the surface of the fibre suspension, and thus ink and impurities can be removed by means of overflow or by scraping.
U.S. Pat. No. 5,465,848 discloses a flotation container. The flotation container includes an injector provided with a feed pipe for introducing a fibre suspension flow into the flotation container and for mixing air into the fibre suspension flow. In addition to the feed pipe, the injector comprises an aperture plate for dividing the fibre suspension flow to be fed into the flotation container into smaller partial flows. Downstream of the aperture plate and at a distance from it, there are pipe sections which form a mixing apparatus and where the partial flows of the fibre suspension flow entering through the apertures of the aperture plate and air are pre-mixed into each other. An air fitting is arranged between the aperture plate and the pipe sections on the side of the injector. The air fitting is used to introduce air to be mixed with the fibre suspension flow into the injector, whereby the air to be introduced into the injector is carried by the partial flows into the mixing devices forming a pre-mixing phase.
A problem associated with the injector described in U.S. Pat. No. 5,465,848 is the difficulty of feeding a sufficient amount of air into the injector in particular for the partial flows of the fibre suspension flow that are formed in the middle section of the aperture plate. It is difficult for the air to be fed through the air fitting on the side of the injector to reach the partial flows of the fibre suspension flows that are formed in the middle section of the aperture plate. In the course of time, this problem will be emphasized as pulp splashes block the space where air is fed between the aperture plate and the pipe sections.